Optical disc apparatus for recording and/or reproducing information on/from an information surface of a rotatable optical disc

ABSTRACT

An optical disc apparatus ( 1 ) for recording and/or reproducing information on/from an information surface ( 3 ) of a rotatable optical disc ( 5 ). The apparatus comprises a supporting assembly ( 7 ), a spindle motor ( 15 ), associated with the supporting assembly ( 7 ), having a spindle ( 17 ) with a spindle axis ( 19 ) for rotating the optical disc ( 5 ), an optical lens unit ( 21 ) associated with the supporting assembly ( 7 ) for scanning an information surface ( 3 ) of said optical disc ( 5 ) mounted on the spindle ( 17 ), and comprising a focussing lens assembly ( 23 ), a swing arm assembly ( 35 ) which is rotatable about a swing axis ( 39 ), comprising movable magnetic a focussing means ( 45 ) provided near a free end ( 37 ) of the swing arm assembly ( 35 ), for driving the said focussing lens ( 29 ) along said focussing axis ( 31 ) so as to focus said optical beam ( 33 ) on the optical disc information surface ( 3 ), and stationary magnetic focussing means ( 46 ) magnetically cooperating through an intermediate air gap ( 48 ) with the movable focussing means ( 45 ). The stationary and movable magnetic focussing means ( 46,45 ) are disposed and cooperate with the movable magnetic focussing means such that the force vector component (P) intersects a focussing lens area ( 27 ) bounded by a focussing lens periphery ( 29 ).

The present invention relates to an optical disc apparatus for recordingand/or reproducing information on/from an information surface of arotatable optical disc.

An optical disc apparatus of the kind indicated above is known from U.S.Pat. No. 6,052,357. This document describes an optical disc apparatusfor recording and/or reproducing information on/from an informationsurface of a rotatable optical disc, comprising a supporting assemblyand a spindle motor, associated with the supporting assembly, having aspindle with a spindle axis for rotating the optical disc, mounted onthe spindle, about the spindle axis. An optical lens unit is associatedwith the supporting assembly in order to scan an information surface ofthe optical disc mounted on the spindle. The optical lens unit comprisesa focussing lens assembly having a movable focussing lens having afocussing lens area bounded by a focussing lens periphery and afocussing axis intersecting the focussing lens area, which focussinglens assembly is adapted to focus an optical beam on the informationsurface of the optical disc. A swing arm assembly is provided whichcomprises a generally elongate swing arm structure, the focussing lensassembly being mounted at a free end thereof. The swing arm assembly isrotatable about a swing axis spaced from the free end and directedgenerally perpendicular to the swing arm structure and generallyparallel to the spindle axis and the focussing axis, such that the swingarm assembly sweeps a plane generally parallel to the informationsurface of the mounted optical disc, the swing arm assembly therebycausing the focussing lens assembly to scan over the information surfaceof the mounted optical disc. The swing arm assembly also comprisesmovable magnetic focussing means, near the free end of the swing arm,associated with the swing arm assembly for driving the focussing lensalong the focussing axis to focus the optical beam on the optical discinformation surface.

In order to focus the optical beam on the optical disc informationsurface, this known optical disc apparatus also comprises stationarymagnetic focussing means, associated with the supporting assembly, whichmagnetically cooperates through an intermediate air gap with the movablefocussing means in order to generate a magnetic force vector having avector component parallel to the focussing axis of the focussing lensassembly so as to drive the focussing lens assembly along the focussingaxis by electromagnetic force.

In this prior art optical disc apparatus, the movable magnetic focussingmeans are comprised of magnetic focussing coil means disposed in a planewhich is generally parallel to the focussing axis of the focussing lensat the free end of the swing arm structure, at a location spaced fromthe focussing lens assembly at the remotest part of the swing armstructure as seen from the swing axis thereof. Focussing movements ofthe focussing lens assembly in a direction according to its focussingaxis are enabled by the fact that the swing arm structure comprises twospaced elongate, generally parallel flat resilient arm elementsextending between the swing axis and the focussing lens assembly, thatis, interconnected at or near the free end of the swing arm assembly.The stationary magnetic focussing means cooperate with theabove-mentioned magnetic coil means over an air gap which is generallyparallel to the magnetic coil means and, therefore, generally parallelto the focussing axis of the focussing lens.

Any magnetic force vector acting through the air gap on the focussingcoil of the movable magnetic focussing means of the prior artarrangement described will exert on the focussing lens not only a forcealong the focussing axis, but also a perpendicular force. Moreover,these forces act on the focussing lens assembly and, therefore, on theswing arm assembly at some distance from the focussing axis of thefocussing lens, resulting in force moments exerted on the resilient armelements of the swing arm assembly. Thus, eccentric forces and momentsare dynamically produced during the focussing of the focussing lens;this will produce dynamic reaction forces and moments in the swing armassembly which may cause undue vibrations and distortions as well asadded loading of the swing arm spindle. Undesirable parasitic resonancemay result in the direction along the focussing axis, upsetting theautomatic focussing control system of the optical lens unit. Alsocrosstalk may arise in the scanning direction perpendicular to thefocussing direction, upsetting the automatic scanning control system.

It is an object of the invention to provide an optical disc apparatuswhich exhibits improved dynamic behavior by mitigating the occurrence ofany undue eccentric dynamic focussing forces exerted on the movablemagnetic focussing means. This object is achieved by the optical discapparatus of the invention which comprises

-   -   a supporting assembly;    -   a spindle motor, associated with the supporting assembly, having        a spindle with a spindle axis for rotating an optical disc        supported by the spindle about the spindle axis;    -   an optical lens unit associated with the supporting assembly for        scanning an information surface of said optical disc, and        comprising:    -   a focussing lens assembly with a movable focussing lens having a        focussing lens area bounded by a focussing lens periphery and a        focussing axis intersecting said focussing lens area, said        focussing lens assembly being adapted for focussing an optical        beam on said information surface;    -   a swing arm assembly comprising a generally elongate swing arm        structure supporting said focussing lens assembly at a free end,        the swing arm assembly being rotatable about a swing axis spaced        from said free end and directed substantially perpendicularly to        the swing arm structure and generally parallel to said spindle        axis, the swing arm assembly also comprising a movable magnetic        focussing means provided near said free end of the swing arm        assembly for driving said focussing lens along said focussing        axis so as to focus said optical beam on the optical disc        information surface;    -   which optical disc apparatus also comprises:    -   a stationary magnetic focussing means associated with the        supporting assembly for magnetically cooperating, through an        intermediate air gap, with said movable focussing means in order        to generate a magnetic force vector having a vector component        parallel to said focussing axis so as to drive the focussing        lens assembly along said focussing axis, and has the feature,        that the stationary and movable magnetic focussing means are        disposed and cooperate such that the force vector component        intersects the focussing lens area. Because of this feature, the        force vector will be situated near the focussing axis, thus        mitigating the above problems of the prior art arrangements.

Preferably, an embodiment is used wherein the force vector componentgenerally coincides with the focussing axis of the focussing lens. Insuch an embodiment particularly no eccentric forces are exerted on thefocussing lens assembly.

In optical disc apparatus of the kind in which the invention may beadvantageously applied, much of the optical lens unit associated withthe supporting assembly, such as the laser source and the associatedoptical and electronic means necessary to send data to and/or receivedata from the information disc, will be located near the swing axis ofthe swing arm assembly so as to reduce the inertia thereof. The laserbeam will travel along a section of the light path between the focussinglens assembly and the laser source which intersects the focussing axisof the focussing lens assembly perpendicularly. In an advantageousembodiment of the invention of the kind in which the laser beamintersects the focussing axis perpendicularly the optical lens assemblycomprises, near the free end of the arm assembly, a perpendicularlyreflecting optical element connected to the focussing lens, having areflective surface on the side of the focussing lens which is directedaway from the information surface of a mounted optical disc and causesreflection of a laser beam travelling in the general direction betweenthe swing axis and the focussing axis so as to travel through thefocussing lens generally along the focussing axis, and the movablemagnetic focussing means are connected to the reflecting element in aposition in the side of the reflecting surface which is directed awayfrom the movable focussing lens. The magnetic focussing means can thusbe positioned on the focussing axis of the focussing lens.

The previous embodiment may be advantageously combined with a furtherembodiment of the invention, wherein the swing arm assembly is boundedby spaced virtual parallel flat planes extending perpendicularly to theswing axis, a first plane being nearer to a mounted optical disc and asecond plane being more remote from a mounted optical disc; at least aportion of the reflecting element is inwardly spaced from the secondplane, so that an intermediate space is provided between the reflectingelement and the second plane, and the stationary magnetic focussingmeans extend into the intermediate space between the reflecting elementand the second plane, thus occupying at least a portion of theintermediate space. This embodiment will contribute to minimizing thespace requirements for the movable and stationary magnetic focussingmeans. Reduction of the overall dimension of optical disc apparatus,particularly for data storage, is highly desirable in order to increasethe field of use to the incorporation in ever smaller informationtechnology and communications devices. Interesting in this respect is afurther embodiment, wherein the movable and stationary magneticfocussing means cooperate through an air gap which is generally parallelto the reflecting surface of the reflecting element.

To minimize the inertia of the optical lens unit and the overalldimensions of the optical disc apparatus, the latter embodiment may becombined with a further embodiment, wherein the reflecting surface ofthe focussing lens assembly is disposed in an inclined plane relative tothe swing axis of the swing arm assembly, the movable electricalmagnetic coil means being disposed generally in an inclined planeparallel to the reflecting surface, and the stationary magnetic circuitmeans comprising an inclined face directed towards the movableelectrical magnetic coil means, such that the air gap between themovable electrical magnetic coil means and the stationary magneticcircuit means is disposed in an inclined plane generally parallel to theinclined reflective surface of the focussing lens assembly.

To reduce the inertia of the swing arm assembly and to provide resilientguidance means for the focussing lens assembly, in a further embodimentof the invention the swing arm structure comprises two spaced elongategenerally parallel flat resilient arm elements which extend between theswing axis and the focussing lens assembly and are interconnected at ornear the free end of the swing arm assembly by the focussing lensassembly.

The embodiments of the apparatus according to the invention aredisclosed in detail in the claims 2 to 8.

The objects and features of the present invention will become moreapparent by referring to the following non-limiting description of apreferred embodiment, given with reference to the accompanying drawingsin which:

FIG. 1 is a schematic side elevation of an embodiment of an optical discapparatus according to the invention;

FIG. 2 is a plan view of a section of the optical disc apparatus of FIG.1; and

FIG. 3 is an enlarged schematic side elevation a in cross-sectional viewshowing details of the focussing lens assembly and the associatedmovable and stationary magnetic focussing means of the optical discapparatus of the FIGS. 1 and 2.

The drawings are of a schematic nature and intended for illustrativepurposes only. The details in the figures are drawn to an arbitraryscale which may be different from the overall scale. The same componentsare indicated by the same reference number throughout the figures.Components and assemblies which may be configured according toprinciples which are basically known from the prior art will not bediscussed in detail.

The FIGS. 1 and 2 show an overall configuration of an optical discapparatus 1 for recording and/or reproducing information on/from aninformation surface 3 of a rotatable optical disc 5. The apparatuscomprises a supporting assembly 7 with side walls 9,11 and a bottom wall13. The supporting assembly is only partly shown and may be of anarbitrary configuration, but in many cases it will be generally boxshaped. A spindle motor 15 is provided on the bottom wall 13 of thesupporting assembly 7; this motor has a spindle 17 with a spindle axis19 for rotating the optical disc 5 about the spindle axis 19. Theoptical disc may be mounted on or put on and/or clamped to the spindle.

An optical lens unit 21 is provided on a raised part 22 provided on thebottom surface 13 of the supporting assembly 7 in order to scan theinformation surface 3 on the bottom side of the optical disc 5 mountedon the spindle 17. The optical lens unit 21 comprises a focussing lensassembly, generally referred to as 23, having a movable focussing lens25 having a focussing lens area 27 bounded by a focussing lens periphery29 and a focussing axis 31 intersecting the focussing lens area, thefocussing lens assembly 23 being adapted for focussing an optical beam33 on the information surface 3 of the optical disc 5. The focussingaxis 31 is substantially parallel to the spindle axis 19.

A swing arm assembly 35 is provided which is configured as a generallyelongate swing arm structure supporting the focussing lens assembly 23at a free end 37. The swing arm assembly is rotatable about a swing axis39 spaced from the free end 37 and directed generally perpendicularly tothe swing arm structure and generally parallel to the spindle axis 19and the focussing axis 31, such that the swing arm assembly 35 sweeps aplane generally parallel to the information surface 3 of the mountedoptical disc 5, the swing arm assembly 35 thereby causing the focussinglens assembly 23 to scan over the information surface 3 of the mountedoptical disc 5. In the embodiment shown in the drawings a swing armspindle 41 is provided for the swing arm assembly on the raised part 22.The swing arm assembly has a generally two-armed configuration having asecond free end 43 remote from the free end 37. The spindle 41 isdisposed between the free ends 37 and 43.

The swing arm assembly 35 also comprises movable magnetic focussingmeans 45 provided near the free end 37 for electromagnetically drivingthe focussing lens 25 along the focussing axis 31 so as to focus theoptical beam 33 on the optical disc information surface 3. In thepresent embodiment the moving magnetic focussing means consist, in amanner which is known per se, of a generally annular focussing coil 45having turns of conductive wire such as copper wire. The focussing coil45 may have a generally oval or rectangular shape, such as is well knownin the art, and is shown in a cross sectional view in FIG. 3.

The optical disc apparatus 1 also comprises stationary magneticfocussing means 46 associated with the supporting assembly 7 formagnetically cooperating, through an intermediate air gap 48, with themovable focussing means 45 so as to generate a magnetic force vectorhaving a vector component F which is parallel to the focussing axis 31,thus driving the focussing lens assembly 23 along the focussing axis 31.In the present embodiment the stationary magnetic focussing meansconsist, in a manner well known in the art, of a vertically magnetizedpermanent magnet 57 which is bounded by ferromagnetic flux concentratingupper and lower yoke plates 59 and 61, respectively, which are mountedan a lower support of a suitable magnetically isolating material.

The stationary and movable magnetic focussing means 45,46 are disposedand cooperate such that the force vector component P intersects thefocussing lens area 27 bounded by the focussing lens periphery 29. Infact, in the embodiment shown in the drawings, the force vectorcomponent P generally coincides with the focussing axis 31 of thefocussing lens 27.

The optical lens assembly 23 comprises, near the free end 37 of the armassembly, a perpendicularly reflecting optical element 47 which isconnected to the focussing lens 27 and is integral therewith in thepresent embodiment; it is made of an optical grade transparent syntheticresin material so as to form an integral optical component having areflecting surface 49 on one side which reflects the optical beam 33 bytotal inner reflection. This reflective surface 49 is disposed on theside of the focussing lens 25 which is directed away from theinformation surface 3 of a mounted optical disc 5 and causes reflectionof the laser beam 33, travelling in the general direction between theswing axis 39 and the focussing axis 31, so as to travel through thefocussing lens 25 generally along the focussing axis 31. The movablemagnetic focussing means 45 are connected to the reflecting element 47in a position on the side of the reflecting surface 49 which is directedaway from the movable focussing lens 25.

The swing arm assembly is bounded by spaced virtual parallel flat planes51,53 (symbolically shown as dashed lines in section in FIG. 3)extending perpendicularly to the swing axis 39, a first plane 51 beingnearer to a mounted optical disc 5 and a second plane 53 being moreremote from a mounted optical disc 5.

The reflecting element 47 is inwardly spaced from the second plane 53 sothat an intermediate space 55 is provided between the reflecting element47 and the second plane 53. The stationary magnetic focussing means 46extend into this intermediate space 55 between the reflecting element 47and the second plane 53, thus occupying a portion of the intermediatespace 55.

The movable and stationary magnetic focussing means 45,46 cooperatethrough an air gap 48 which is generally parallel to the reflectingsurface 49 of the reflecting element 47. In fact, the focussing coil 45is fixed on the outer surface of the reflecting element 47 using asuitable adhesive material which does not degrade the inner reflectiveproperties of the reflective surface 49. Preferably, the reflectingsurface 49 is optically isolated by a suitable material such as a metallayer deposited by vacuum deposition.

The reflecting surface 49 of the focussing lens assembly 23 is disposedin an inclined plane relative to the swing axis 39 of the swing armassembly 35. The movable electrical magnetic coil means 45 are disposedgenerally in an inclined plane parallel to the reflecting surface 49 andthe stationary magnetic circuit means 46 comprise an inclined face 65directed towards the movable electrical magnetic coil means 45, suchthat the air gap 48 between the movable electrical magnetic coil means45 and the stationary magnetic circuit means 46 is disposed in aninclined plane generally parallel to the inclined reflective surface 49of the focussing lens assembly 23.

The swing arm structure comprises two spaced elongate generally parallelflat resilient arm elements 67,69 which extend between the swing axis 39and the focussing lens assembly 23 and are interconnected at or near thefree end 37 of the swing arm assembly 35 by the focussing lens assembly23.

At the end of the swing arm structure which is remote from the focussinglens assembly 23 a magnetic system of a general kind known per se fromthe prior art is provided to drive the swinging movements of the swingarm assembly 35 about the intermediate swing axis 41. This magneticsystem is not in itself part of the invention and, therefore, is notshown in detail in the drawings. It comprises an electrical coil 73attached to the free end 43 of the swing arm structure, as well as acooperating stationary permanent magnetic circuit associated with thesupporting assembly 7. This circuit is denoted merely symbolically inthe drawings by dashed lines and bears the general reference number 71.

The central part 75 of the swing arm assembly 35 may be hollow andbox-shaped and may contain components of the optical system cooperatingwith the focussing lens assembly 23 and the reflecting surface 3 of theoptical disc 5, such as a semiconductor laser generating the laser beam33, as well as further associated optical and electronic means formodifying the properties and the direction of the laser beam, forprocessing signals, etc.

Thus, an optical disc apparatus has been described according to a bestmode for carrying out the invention contemplated by the inventor at thetime of writing the present specification. It will be appreciated bypersons skilled in the art that the invention is not limited by what hasbeen specifically described and shown above. Many modifications arepossible without departing from the inventive concepts disclosed herein.The swing arm assembly need not be of the two-arm type but could be ofthe one-arm type having its swing axis situated at one end of the swingarm assembly. The focussing lens assembly need not be suspended in leafsprings of a swing arm structure. Instead the swing arm structure couldbe rigid and the focussing lens assembly could be mounted resiliently onthe rigid structure. The total height dimension of the optical discapparatus could be reduced by suitable measures to reduce the heights ofthe raised portion 22 of the arm spindle support as well as of thesupport 63 of the stationary magnetic means 46 as much as possible. Ifminimal overall dimensions are preferred, preferably the whole swing armassembly could be comprised between the virtual planes 51,53 of theswing arm structure. The integrated focussing lens assembly could bereplaced by a multiple component assembly including a separate mirrorhaving an exterior reflective surface instead of the inner totallyreflecting surface 49. The movable magnetic focussing could be disposedin a plane other than the plane of the reflecting surface 49 and at adifferent angle. For example, use could be made of a vertically disposedmagnetic coil located beneath the focussing lens assembly 23 cooperatingwith a stationary magnetic circuit having a central vertical curved slotin which the magnetic coil can move.

1. An optical disc apparatus for recording and/or reproducinginformation, comprising: a supporting assembly; a spindle motor,associated with the supporting assembly, having a spindle with a spindleaxis for rotating an optical disc supported by the spindle about thespindle axis; an optical lens unit associated with the supportingassembly for scanning an information surface of said optical disc, andcomprising: a focussing lens assembly with a movable focussing lenshaving a focussing lens area bounded by a focussing lens periphery and afocussing axis intersecting said focussing lens area, said focussinglens assembly being adapted for focussing an optical beam on saidinformation surface; a swing arm assembly comprising a generallyelongate swing arm structure supporting said focussing lens assembly ata free end, the swing arm assembly being rotatable about a swing axisspaced from said free end and directed substantially perpendicularly tothe swing arm structure and generally parallel to said spindle axis, theswing arm assembly also comprising a movable magnetic focussing meansprovided near said free end of the swing arm assembly for driving saidfocussing lens along said focussing axis so as to focus said opticalbeam on the optical disc information surface; the optical disc apparatusalso comprising: a stationary magnetic focussing means associated withthe supporting assembly for magnetically cooperating, through anintermediate air gap, with said movable focussing means in order togenerate a magnetic force vector having a vector component parallel tosaid focussing axis so as to drive the focussing lens assembly alongsaid focussing axis, the stationary and movable magnetic focussing meansbeing disposed and cooperating such that said force vector componentintersects said focussing lens area.
 2. An optical disc apparatus asclaimed in claim 1, wherein said force vector component generallycoincides with the focussing axis of said focussing lens.
 3. An opticaldisc apparatus as claimed in claim 1, wherein the optical lens assemblycomprises, near said free end of the arm assembly, a perpendicularlyreflecting optical element connected to the focussing lens, having areflective surface on the side of the focussing lens which is directedaway from the information surface of the optical disc, when supported bythe spindle, and causes reflection of a laser beam travelling in thegeneral direction between the swing axis and the focussing axis so as totravel through the focussing lens generally along the focussing axis,and the movable magnetic focussing means are connected to the reflectingelement in a position on the side of said reflecting surface which isdirected away from the movable focussing lens.
 4. An optical discapparatus as claimed in claim 3, wherein the swing arm assembly isbounded by spaced virtual parallel flat planes extending perpendicularlyto the swing axis, a first plane being nearer to the optical disc, whensupported by the spindle, and a second plane being more remote from saidoptical disc; at least a portion of the reflecting element is inwardlyspaced from said second plane, so that an intermediate space is providedbetween the reflecting element and said second plane; and the stationarymagnetic focussing means extend into said intermediate space between thereflecting element and said second plane, thus occupying at least aportion of said intermediate space.
 5. An optical disc apparatus asclaimed in claim 2, wherein the movable and stationary magneticfocussing means cooperate through an air gap which is generally parallelto said reflecting surface of the reflecting element.
 6. An optical discapparatus as claimed in claim 1, wherein the stationary magneticfocussing means are configured as arcuate permanent magnetic circuitmeans and the movable magnetic focussing means are configured aselectrical magnetic coil means.
 7. An optical disc apparatus as claimedin claim 6, wherein the reflecting surface of the focussing lensassembly is disposed in an inclined plane relative to the swing axis ofthe swing arm assembly; said movable electrical magnetic coil means aredisposed generally in an inclined plane parallel to the reflectingsurface; and said stationary magnetic circuit means comprise an inclinedface directed towards said movable electrical magnetic coil means, suchthat the said air gap between said movable electrical magnetic coilmeans and said stationary magnetic circuit means is disposed in aninclined plane generally parallel to said inclined reflective surface ofthe focussing lens assembly.
 8. An optical disc apparatus as claimed inclaim 1, wherein the swing arm structure comprises two spaced elongategenerally parallel flat resilient arm elements which extend between theswing axis and the focussing lens assembly, and are interconnected at ornear the free end of the swing arm assembly by the focussing lensassembly.